This invention relates to tool steels and, more particularly, to a hot work tool steel having improved wear resistance, and toughness, as well as good temper resistance, tensile properties and dimensional stability.
Hitherto, a hot work tool steel designated as AISI Type H13 has been extensively used in the aluminum extrusion industry to provide mandrels and dies for use at temperatures in the range of 700-1000 F. (370-540 C.). Type H13 alloy steel has the following composition in weight percent (w/o). Here and throughout this application, percent will be by weight unless otherwise indicated.
______________________________________ w/o ______________________________________ C 0.32-0.45 Mn 0.20-0.50 Si 0.80-1.20 Cr 4.75-5.50 Mo 1.10-1.75 V 0.80-1.20 Fe Bal. ______________________________________
Included with the balance (Bal.) are the usual incidental amounts of other elements present in commercial grades of tool and die steels.
Type H13 is nominally designated as a 5 Cr hot work die steel and is noted for its toughness and wear resistance. Its other properties include good temper resistance, and high hardness and strength at the above-mentioned elevated temperatures. It is deep hardening, can be hardened in large sections by air cooling, and can be heat treated to an ultimate tensile strength of up to about 300 ksi (2070 MPa). However, because of its tendency to undergo a substantial loss of toughness as measured by the Charpy V-notch impat test when members of large section size are air cooled, Type H13 leaves much to be desired. Charpy V-notch impact values of less than about 2 ft-lb (about 2.7 J) in the longitudinal direction are usual for air cooled type H13 members of large section size, that is, section sizes of six inches and larger.